1. Field of the Invention
This invention relates generally to digital image correction. More specifically, the present invention relates to reducing motion artifacts in a subtracted image. In particular, the present invention is directed to a method for calculating a pixel-shift vector that predicts the motion in dynamic image data and can be used to shift reference image data in order to generate a subtracted image with reduced motion artifacts.
2. Background Discussion
In digital subtraction angiography, contrast medium is injected into blood vessels and real-time subtraction of pre- and post-contrast images is performed. Typically, when reference image data (pre-contrast) and dynamic image data (post-contrast) are subtracted from one another, the resultant subtracted image contains motion artifacts. These motion artifacts result from motion in the dynamic image data which causes the dynamic image data to shift relative to the reference image data.
Movement by the doctor, patient, or equipment may cause the live frame to shift from the position it was in when the reference or mask frame was captured. Subtracting the shifted live frame from the roadmap mask will result in artifacts in the subtracted image. Conventional methods attempt to reduce artifacts by shifting the mask frame using a pixel-shift vector determined as a function of a previously captured live frame and the mask frame. While this approach may reduce artifacts to an extent, it will also lag behind the actual motion in the live frame.
Conventional techniques attempt to overcome motion artifacts in subtracted angiography images by shifting the mask frame (pre-contrast) using a vector that has been calculated based on a past frame of the x-ray image. Two such conventional methods are described in U.S. Pat. No. 4,558,462 issued to Horiba et al. and U.S. Pat. No. 4,870,692 issued to Zuiderveld et al., which are both incorporated by reference in their entirety herein. However, if the motion in the current frame of the x-ray image differs from the motion in the past frame of the x-ray image from which the displacement vector was calculated, then the displacement vector will not be correct for the current x-ray image and artifacts will still result in the subtracted image.
Therefore, it would be an advancement in the state of the art to provide a system and method of calculating a pixel-shift vector that adjusts the reference image data of the current frame of the live x-ray image based on previously calculated pixel-shift vectors.
It would also be an advancement in the state of the art to provide improved reduction in motion artifacts in a resultant image.
It would also be an advancement in the state of the art to increase the clarity of the subtracted image in a digital subtraction angiography.